Cob is an earth construction type widespread in Normandy. In this study, thermal and hygrometric behaviour of cob is studied. Two different mixes currently used for cob constructions are used. Several cob formulations are developed by varying fibre content as well as soil mixes. Results show that a higher fibre content leads to a lower thermal conductivity due to thermal conductivity of wheat straw and cob smaller density. Results about hygrometric properties show that knowing hygrometric properties of each component allow to predict cob hygrometric properties. Knowing hygrometric properties allow to determine cob behaviour variation during the building life.